Generally speaking, the phenomenon of intumescence using silicone rubber matrices is already known and has been set forth in the prior art. A typical reference is U.S. Pat. No. 5,047,449 issued to Pastureau, Sep. 10, 1991, for a fire protection material. The patentee provides a intumescent composition which includes a silicone elastomer (RTV-121) a reinforcing charge of a metal oxide, borax and an insulative charge of mica or vermiculite.
U.S. Pat. No. 5,262,454, issued to Leroux et al., Nov. 16, 1993, teaches a flame resistant polyorganosiloxane compound containing hollow glass balls and intumescent compound. The composition indicated in the disclosure includes the use of a relatively high percentage of hollow glass balls containing a non-combustible gas.
Further prior art in this area of technology includes European Patent Application 508751-A2, which teaches the use of a sodium silicate and expandable graphite in an aqueous system with a polyvinyl alcohol binder.
To effectively meet fire, temperature and hose stream requirements of ASTM Standard E-814, the release and amplitude of the intumescence must be controlled and limited. The use of a silicone binder has been generally considered advantageous in view of the fact that there is no production of toxic pyrolysis products in the case of fire.
Further prior art related to this art is Japanese Patent publications JP 0415169 and JP 04145178. These references generally refer to the combination of sodium silicate and foamed or sponge-like graphite powders for use in heat resistant coatings. Silicone and aluminum phosphate compounds have also been set forth as suitable binders for use in intumescent compositions.
Having regard to the intumescent compositions that have been previously set forth in the prior art, there exists a need for an intumescent composition which when used as firestop material around combustible pipe, such as PVC or ABS, readily meets the test criteria set forth under ASTM Standard E-814.